The invention concerns a method of making a compensation shaft out of a drop-forged shaft blank. The compensation shaft comprises a shaft section with a mass center of gravity which extends eccentric to the axis of rotation of the compensation shaft and which, together with the axis of rotation of the compensation shaft, creates an unbalanced mass plane which extends substantially perpendicularly to the die parting plane. The shaft section comprises a base body and a rib with a height H starting from the base body and extending, with regard to the axis of rotation, in a direction of the unbalanced mass plane oriented away from the mass center of gravity.
A compensation shaft of the above-noted type is used in internal combustion engines for providing a partial or complete compensation of the free mass forces and/or mass torques. The radial mounting of the compensation shaft is increasingly accomplished through low-friction needle roller bearings that are in direct rolling contact with the bearing journal of the compensation shaft, so that needle roller-mounted compensation shafts are generally configured as forgings with a high tribological load bearing capacity. This is also the case in DE 10 2007 019 008 A1 in which, with a view to a homogenous fiber orientation in the region of the highly loaded tribological load zone of the bearing journal, it is proposed to orient the parting plane of the die in a direction perpendicular to the unbalanced mass plane of the compensation shaft.
The shaft sections extending between and next to the bearing journals and decisively participating in the unbalanced mass action of the compensation shaft comprise stiffening ribs in direction of the unbalanced mass plane, which ribs are formed through the hollow mold of one of the die halves because the die parting plane extends perpendicularly to the unbalanced mass plane. This flow of material, known in forging techniques as swelling, occurs in opposition to the lift movement of the die halves and, with a view to completely filling the hollow rib mold, it is required that a sufficient volume of material be available also in direction of the die parting plane, which material volume is pressed under very high pressure on the one hand in direction of the hollow rib mold and on the other hand in direction of the ridge gaps of the die with formation of the forging ridges. Consequently, the forgeable height of the rib, i.e. its extent in direction of the unbalanced mass is limited by the width of the forged shaft blank, which width extends in direction of the die parting plane.